Incentives matter.  Reward people for certain actions, and people will do whatever they can to get the reward.  Baseball is no exception- when certain rules change, people modify their behavior to obtain optimal results under the new rule.
What follows is a thought experiment on one (of many) possible (and perhaps far-fetched) cause of the incentives to take steroids, and the apparent solution- stadium design.

With relation to steroids, the big reward that drove many players to bulk up was the fame and fortune that came with being a franchise slugger.  Most players and fans agree that steroids do not help the hand-eye coordination needed to hit a ball, but extra muscle means you can hit the ball further.  What is lost in return for the extra muscle obtained through steroid use?  Usually speed and health, particularly of joints and bones.
Look at everyone's favorite steroid poster boy, Bonds.  Everyone agrees he was a great ballplayer, probably a hall of famer, before he suddenly became muscle-bound slugger.  (Compare his build with the picture in this article.)  He was also fairly speedy- SB in the 30s, 5-7 triples per year.  His speed numbers dropped off to < 15 steals as his power numbers went up, as his SLG went from 500 or 600 up to 700 or 800.  (Surprisingly, his zone rating as an outfielder didn't change that much.)
So presumably people who take steroids will trade speed for power.  The most obvious reward for power is the home run, while the reward for speed is the stolen base and some more extra base hits.  Has anything happened in the last 10-20 years that would make home runs easier to obtain while diminishing the need for speed?
Part of the idea for this diary came from someone mentioning the crazy dimensions of the polo grounds yesterday.  If you browse through the stadium dimensions here, you can see what most people are aware of- recent stadium designs have been more "intimate," or bandboxes as some call them.  The result is more homers hit out of the park, and less need to leg out extra base hits.  Compare that to places like the polo grounds (very short lines, but 450 to the alleys) or the old Yankee stadium dimensions (short porch, but 450 to left center.)
The numbers bear this out- there are about 15-20 inside the park homers each season in the modern era, while Ty Cobb had 49 in his career and 9 in one season.  The records for triples are also way back in the early 1900s.  In this era, anything not hit to an outfielder is usually a double unless it takes a weird bounce or the batter is very fast- triples are more rare, in ITPHRs are highlight reel material.
So there is no need to be fast as long as you can hit the ball 400 feet- whereas being a slug or standing and admiring your hits (a la Manny) would earn you a 400 foot single (not to mention a fastball in your ear) in the old ballparks.  Steroid use plays right into this- your knees might give out, but you can crawl around the bases if you can hit the ball far enough, so who needs to run?  Larger outfields would also mean that you can't stick a juiced up slugger with bad knees in the outfield because it will cost you on defense (although the Bonds' ZR numbers don't necessarily support this.)  Consequently, players are willing to sacrifice their speed if they can have more muscle.  Obviously, this doesn't address pitchers who take steroids, but most of the focus these days is on sluggers.
The obvious solution is to return to larger stadium dimensions.  There is no way this will ever happen, since fans like the smaller stadiums and larger HR numbers.  Perhaps there is some other rule change that could have a similar effect, though; if baseball can return to a greater emphasis on speed and less on power, it might discourage the next generation of players from focusing on the almighty HR.  Or they might just search for the miracle drug that will let them hit the ball 500 feet instead of 400.